Cloud dispersion of fine plastic powder



Nov. 28, 1967 .1.J. QuAcKx-:NBUSH ETAL 3,354,865

CLOUD DISPEBSION OF' FINE PLASTIC POWDER Filed April 12, 196e INVENTOR.JOHN J. QUACKENBUSH HERBERT O. CORBETT United States Patent O CLOUDDISPERSION F FINE PLASTIC POWDER John J. Quackenhush, Monroe, andHerbert O. Corbett, Bridgeport, Conn., assignors to National Distillersand Chemical Corporation, New York, N .Y., a corporation of VirginiaFiled Apr. 12, 1966, Ser. No. 542,040 2 Claims. (Cl. 118-309) Thisinvention relates to an apparatus for the handling and deposition of nemicro size plastic powder, and more specically relates to a novelapparatus for the even deposition of nely ground thermoplastic microsize powders of varying densities and varying particle sizes on a web.

The powder coating of webs of plastic material or paper, or the like, iswell known to the art. In such arrangements, a stationary or moving baseweb is to have deposited or dusted thereon a suitable powder with theweb and powder later being operated upon to cause the line thermoplasticparticles to melt and fuse to the web. Thus the coated web can be passedthrough an oven and subjected to temperatures which will cause thethermoplastic particles to melt and fuse to form an intimate bond and acontinuous or non-continuous type coated surface as desired.

The materials can be further press nipped under -pressure as by heatedor chilled rolls to force the particles down into the web and provide,if desired, high gloss surfaces or intimate bonding of bers offabric-like materials.

Considerable -diilculty has been experienced in the past to properlysuspend and evenly deposit very nely ground thermoplastic powders ofvarying densities in the range of .910 to .965 and varying particlesizes of from 2 to 100 microns.

The principle of the present invention is to provide a novel apparatusfor uniformly applying fine thermoplastic powders inthe dry form to astationary or moving web for the purpose of providing heat scalable,water resistant, high gloss or ber bonding type coatings to the websurface.

The most common method for handling fine particle size dust or powderhas been with the use of a fluidized bed. While this method isacceptable for controlling the dispersion of relatively large particlesize powders, a number of difficulties are encountered when attemptingto use a fluidized bed arrangement with extremely small diameterparticles which are in the range of from 2 to 100 microns. Thus, whensuch small particles are used there will be erratic feed, unbalanceddispersion levels, and lack of control of the deposition.

The present invention provides a novel system wherein a cloud of fineparticles can be supplied to and suspended in controlled averagedensities Vin a novel equilibrium cloud chamber. Suitable exit supplylines communicate from the equilibrium cloud chamber to a settlingchamber which receives the web with the flow of micron size particlesthrough the system including an average distribution of particles movingto a settling chamber.

It is, therefore, a primary object of this invention to provide a flowof micro size particles to a web where the flow includes an averagemixture of particle density and size.

Yet another object of this invention is to provide a novel clouddispersion arrangement for the deposition of plastic powders having aparticle size range of from 2 to 100 microns and a density range of from.910 to .965.

A further object of this invention is to provide a novel apparatus forcontrolling the dispersion of extremely small powder particles ofthermoplastic material.

Yet another object of this invention is to provide a novel dustingapparatus for dusting micro powders on a web which has a highlycontrolled feed and unbalanced dispersion level. l

These and other objects of this invention will become apparent from thefollowing description taken in connection with the drawing whichschematically illustrates the apparatus used with the novel invention.

Referring now to the drawing, there is illustrated a supply hopper 10which contains tine powders which are to be coated on a moving web 11which can be a web of thermoplastic material or any other suitable webserving as a substrate for the powders to be deposited. The supplyhopper is lled with suitable plastic particles such as ground particlesof polyethylene, known as Microthene, a registered trademark oftheNational Distillers and Chemical Corporation, or any other suitabledusting powder having a particle size range of from 2 to 100 micronswith densities in the range of vfrom .910 to .965.

The supply hopper 10 is then connected to a suitable auger feed screw 12which rotates as illustrated, to convey the powder from hopper 10 into asealed supply canister 13. The supply canister 13 is provided with asealed upper cap 14 which carries a vacuum motor 15 therein whichoperates to evacuate the interior of the supply canister 13 throughvalve 16 and out of a discharge outlet 17. The upper cap 14 furtherreceives a conduit 18 which has an extending bale 19 which is connectedto a suitable air intake motor 20 which passes air through a silicagelmoisture trap 21 to insure the application of ltered intake air to thesupply canister 13.

Head 14 is further provided with outlet lines 30 and 31 which areconnected to input conduits 32 and 33 respectively of the equilibriumcloud chamber 34. Note that the input line 31 and its conduit 32terminate at the lefthand end of the cloud chamber 34 which conduit 33empties into the cloud chamber 34 at the right-hand end thereof atdischarge conduit 35.

The equilibrium cloud chamber 34 then has a plurality of outlet lines36, 37, 38 and 39 which each contain control valves 40 through 43respectively and pressure gauges 44 through 47 respectively. The outletlines 36 through 39 are then connected to a settling chamber 48 whichhas an inlet opening 49, and an outlet opening 50 for receiving the web11. Preferably, openings 49 and 50 are sufficiently small to permit theclose control of the pressure within settling chamber 48 with a pressurerelease labrynth 51 connected to opening 50 for the discharge of airpressure so that a constant pressure can be maintained within settlingchamber 48.

In operation and to deposit a predetermined amount of powder on the web11, vacuum unit 15 is turned on and filtered intake air is forcedthrough conduit 18 into the supply chamber 13. The pressure in chamber13 can range from approximately l to 17 inches of water. This overpressure then forces the line powder coming from supply hopper 10 outthrough lines 30 and 31 and into the equilibrium cloud chamber 34 whichis held at a pressure of approximately 0.1 to 7.0 inches of water. Thecloud density of powders maintained within chamber 34 is controlled bythe air intake rate into supply canister 13 where a lower intake airvelocity to canister 13 will provide a lower cloud density within cloudchamber 34 and vice versa.

It has been found that this type arrangement will cause the powderparticles to be held suspended in the cloud chamber even though theyhave a mixed particle size and a mixed density without the selectivesettling of various particle sizes and various particle densities fromthe remainder of the suspended powders.

The powders are then removed from cloud chamber 34 through the conduits36 through 39 by the appropriate opening of their control valves 40through 43. These valves are more particularly adjusted until theirvarious pressure gauges 44 through 47 register the same pressure wherebythe movement of air and the powders contained therein are found to movethrough the conduits with balanced dispersions or equal distribution ofvarious particle sizes and various particle densities. The settlingchamber under these conditions is preferably held at a pressure of about0.1 to 7.0 inches of water, thereby to maintain a completely balancedpressurized system. The particles passing through conduits 36 through 39then deposit on the web 50 as the web passes through settling chamber 48where the web and the particles thereon are subsequently processed inany desired manner.

The `flow rates through the various lines 30, 31 and 36 through 39 can,of course, be affected by the drag coeicient of these lines. Therefore,it is preferable that the interior of these tubes or supply lines offeras little resistance as possible to the tiow of micron particles whichpass therethrough.

Although this invention has been described with respect to its preferredembodiments, it should be understood that many variations andmodifications will now be obvious to those skilled in the art, and it ispreferred, therefore, that the scope of the invention be limited not bythe specific disclosure herein, but only by the appended claims.

The embodiments of the invention in which an exclusive privilege orproperty is claimed are deiined as follows:

1. Apparatus for the dusting of a at elongated web with an evendistribution of powdered particles of varying particle size and varyingdensity; said apparatus comprising a source of said powdered particles;a supply canister comprising a sealed chamber connected to said source;a blower pump means connected to said supply canister for pressurizingthe interior thereof; a controlled source of dry air connected to saidsupply canister for controllably supplying dry air to the pressurizedinterior of said supply canister; an equilibrium cloud chambercomprising a hermetically sealed elongated chamber; a first and secondoutlet channel extending from said supply canister and connected to theinterior of said cloud chamber at first and second spaced portionsthereof; a settling chamber having an input port and output port forpassing a web through the interior of said settling charnber and apressure relief port; said cloud chamber having a plurality of spacedconduits extending from spaced interior portions thereof and extendinginto respectively spaced interior portions of said settling chamber atthe top of said settling chamber and above the web received within saidsettling chamber.

2. The apparatus as set forth in claim 1 wherein said plurality ofspaced conduits extending into said settling chamber have respectivepressure gauge means therein.

References Cited UNITED STATES PATENTS 2,758,564 8/1956 Randall 118-3092,850,214 9/1958 Rooney 222-193 3,205,856 9/1965 Sorensen 118-309 XCHARLES A. WILLMUTH, Primary Examiner.

I. P. McINTOSH, Assistant Examiner.

1. APPARTUS FOR THE DUSTING OF A FLAT ELONGATED WEB WITH AN EVENDISTRIBUTION OF POWDERED PARTICLES OF VARYING PARTICLE SIZE AND VARYINGDENSITY; SAID APPARTUS COMPRISING A SOURCE OF SAID POWDERED PARTICLES; ASUPPLY CANISTER COMPRISING A SEALED CHAMBER CONNECTED TO SAID SOURCE; ABLOWER PUMP MEANS CONNECTED TO SAID SUPPLY CANISTER FOR PRESSUREINZINGTHE INTERIOR THEROF; A CONTROLLED SOURCE OF DRY AIR CONNECTED TO SAIDSUPPLY CANISTER FOR CONTROLLABLY SUPPLYING DRY AIRE TO THE PRESSURIZEDINTERIOR OF SAID SUPPLY CANISTER; AN EQUILIBRIUM CLOUD CHAMBERCOMPRISING A HERMETICALLY SEALED ELONGATED CHAMBER; A FIRST AND SECONDOUTLET CHANNEL EXTENDING FROM SAID SUPPLY CANISTER AND CONNECTED TO THEINTERIOR OF SAID CLOUD CHAMBER AT FIRST AND SECOND SPACED PORTIONSTHEREOF; A SETTLING CHAMBER HAVING AN INPUR PORT AND OUTPUR PORT FORPASSING A WEB THROUGH THE INTERIOR OF SAID SETTLING CHAMBER AND APRESSURE RELIEF PORT; SAID CLOUD CHAMBER HAVING A PLURALITY OF SPACEDCONDUITS EXTENDING FROM SPACED INTERIOR PORTIONS THEREOF AND EXTENDINGINTO RESPECTIVELY SPACED INTERIOR PORTIONS OF SAID SETTLING CHAMBER ATTHE TOP OF SAID SETTLING CHAMBER AND ABOVE THE WEB RECEIVED WITHIN SAIDSETTLING CHAMBER.